Comparative analysis between RQ ‐ PCR and digital droplet PCR of BCL 2/ IGH gene rearrangement in the peripheral blood and bone marrow of early stage follicular lymphoma

BCL 2/ IGH rearrangements were analysed by polymerase chain reaction ( PCR ) at diagnosis in paired peripheral blood ( PB ) and bone marrow ( BM ) samples from 67 patients with stage I/ II follicular lymphoma ( FL ). Real time quantitative PCR ( RQ ‐ PCR ) and digital droplet PCR (dd PCR ) were performed in cases with a major breakpoint region (MBR+) at diagnosis and after localized radiotherapy and rituximab administration in order to investigate the applicability of dd PCR . The overall dd PCR / RQ ‐ PCR concordance was 81·9% (113/138 samples) and 97·5% in the 40/138 with quantifiable disease ( RQ ‐ PCR ≥10 −5 ). At baseline, dd PCR allowed the recovery of a MBR+ marker in 8/18 (44·4%) samples that resulted MBR‐negative/minor cluster region‐negative/minor BCL2 ‐negative by qualitative PCR . Moreover, the tumour burden at diagnosis significantly predicted progression‐free survival ( PSF ) only when quantified by dd PCR . Paired PB and BM samples analysis demonstrated a high concordance in the detection of BCL 2/IGH+ cells by qualitative and quantitative methods; in particular, 40/62 samples were positive by dd PCR (25 PB+/BM+; 9 PB+/BM−; 6 PB−/BM+), with 34/40 (85%) identified by the study of PB only. In conclusion, in localized FL , dd PCR is a promising tool for monitoring minimal residual disease (MRD) that is at least comparable to RQ ‐ PCR and potentially more accurate. PB is a suitable source for serial BCL 2/ IGH MRD assessments, regardless of the methodology utilized.